Ok, maybe I'm reading too much into this because of things that have happened in my life, but here goes.
It seems to me that he was in love with this beautiful woman and she was in love with him. But then it seems like she became a Christian ("Souls claimed and won/ An opiate drugged haze") and so they couldn't be together. He is so desperate without her and loves her so much that he wants to be a Christian too, even though that is anathema to him (For once my lord please help me
Believe in you"). And he can't stop thinking about her and he's so lonely without her and it's so horribly, wonderfully sad.
Ok, maybe I'm reading too much into this because of things that have happened in my life, but here goes.
It seems to me that he was in love with this beautiful woman and she was in love with him. But then it seems like she became a Christian ("Souls claimed and won/ An opiate drugged haze") and so they couldn't be together. He is so desperate without her and loves her so much that he wants to be a Christian too, even though that is anathema to him (For once my lord please help me Believe in you"). And he can't stop thinking about her and he's so lonely without her and it's so horribly, wonderfully sad.